1. Field of the Invention
The present invention relates in general to a lock system for an automotive back door of a type having an auxiliary door hinged thereto, and more particularly to a lock for locking both the back door and the auxiliary door. More specifically, the present invention is concerned with a lock device used as one part of the lock system for locking one of the doors to its associated part.
2. Description of the Prior Art
A so-called "hinged window-mounted hinged door" has been put into practical use as a back door of a delivery van type motor vehicle. The door of this type comprises generally a main door part which is hinged to the vehicle body to open and close a back opening of the vehicle, and an auxiliary door part which is hinged to the main door part to open and close a window opening formed in the main door part. In order to hold these two door parts in their closed positions, various kinds of door lock systems have been hitherer to proposed. One of the lock systems is disclosed in Japanese Patent First Provisional Publication No. 57-191125, which will be outlined in the following in order to clarify the task of the present invention.
Referring to FIG. 16, a so-called "hinged window-mounted door" a is shown as a back door of a delivery van type motor vehicle. The back door a comprises a main door part c hinged at its upper end to a vehicle body b to open and close a back opening of the vehicle, and an auxiliary door part e hinged to the main door part c to open and close a window opening d formed in the same.
In order to releasably hold the main door part c and the auxiliary door part e in their closed positions, first and second lock devices f and g are independently mounted to the back door. Upon request of opening the main door part c, the first lock device f is manipulated to release the main door part c, while, upon request of opening the auxiliary door part e, the second lock device g is manipulated to release the auxiliary door part. That is, in this conventional door lock system, opening operations of the main and auxiliary door parts c and e are independently carried out by respective lock devices f and g.
However, due to the inherent construction, the above-mentioned conventional lock system may induce the following undesirable matters. That is, if, with a baggage h carried on the roof of the vehicle, the main door part c is brought into its open position with the auxiliary door part e opened, it may occur that the auxiliary door part e collides against an edge of the baggage h resulting in breakage of the same. The problems of this type are frequently carried out by absentminded persons.
In order to solve the above-mentioned problem, there has been also proposed a lock system which is designed to prevent one of the two lock devices from assuming its unlatched condition when the other lock device is in its unlatched condition. With this, there occurs no chance that the two doors are opened at the same.